Fun theory Roger, but it doesn't explain why Maya in a crisis situation involving her brother would freeze at the room.
She doesn't know Lynette after all. And even she did it wouldn't justify her reaction in that context.
Okay, as some of you may recall I have a pet theory that Bella and Lynette were friends. I've extrapolated that what has MC so shocked after opening Bella's secret door is seeing a picture of his mother and Bella. The room of course has something else in it or Maya wouldn't be shocked, but MC's shock is for the revelation that Bella knew his mother.
Why is this relevant here? Because the scene DPC has been waiting to create is the flashback of MC's birth and Lynette's death.
Do Bella and Lynette need to have been friends for us to get that flashback in the next episode? No, but getting the revelation and the flashback together at the start of the episode would be one hell of an opening.
So about a year from now (hopefully) I'll be reminding you all that I fucking called it.
I did specifically point out that the room has something else in it to shock Maya. Whatever this is will be the reason Bella keeps the room locked. I firmly believe that Bella is unaware that her old friend was MC's mother. She may even be unaware that Lynette is dead. Lynette's friends being unaware of her death would explain why they have not been part of MC's life. Even if Bella is not one of those friends, Miranda's and Viv's absence requires an explanation. They may not know that Lynette is dead, or they know she is dead but not how it happened, or they may know she died at childbirth but not know the child survived. If Miranda and Viv (and Bella) knew that Lynette's son survived they would have been a part of his life.
In any case as Bella is unaware of the connection she must have other reasons to keep the room locked and these reasons are shocking for Maya to see from the door. However, I don't see that I need to accurately predict what these reasons are as there surely will be enough space for a picture of Bella and Lynette. I do not need to explain why Maya is shocked because there is no reason why she and MC couldn't be shocked by separate things. And of course what shocked Maya may also be shocking to MC. There may be a great many shocking things in there. What I'm saying is that the thing that shocks MC the most is Bella having a picture of his mother. I most definitely am not saying that the picture is the only thing in there.
Well perhaps I should give an explanation for Maya's shock. But this is simply to show that such explanations can coexist with my theory. It is not truly relevant to Bella and Lynette having been friends. So the most popular theory at the moment is a baby room. I will expand it like this. The room has become a clutter room for things that bring back memories for Bella. She emphatically does not want to throw them away, but looking at them on a daily basis is painful for her. These may indeed include nursery furniture for a baby that Bella lost, but there is plenty of room for James's possessions and both pictures and mementos of family and friends. Things that bring up old memories. The memories themselves don't have to be painful as simply being constantly reminded of happier times would make Bella's current life feel worse by contrast. So she keeps the room locked.
Why was it unlocked at the end of ep 11? Well she probably does put up some Christmas decorations in there. I could see her doing that every year. She doesn't want daily reminders, but she doesn't want to forget either. Decorating the house is one of the times in a year she let's the memories come back. She just forgot to lock the door when she was done with the decorating.